Catalyses the final step of tRNA splicing in the yeast Saccharomyces cerevisiae [2]. The reaction takes place in two steps: in the first step, the 2'-phosphate on the RNA substrate is ADP-ribosylated, causing the relase of nicotinamide and the formation of the reaction intermediate, ADP-ribosylated tRNA [6]. In the second step, dephosphorylated (mature) tRNA is formed along with ADP ribose 1''-2''-cyclic phosphate. Highly specific for oligonucleotide substrates bearing an internal 2'-phosphate. Oligonucleotides with only a terminal 5'- or 3'-phosphate are not substrates [1].